Merge pull request #21015 from steveklabnik/gh20852

Link to sections in the book's README.md

Reviewed-by: alexcrichton

Author: bors

src/doc/trpl/README.md

@@ -8,7 +8,7 @@ memory safe without using garbage collection.
 "The Rust Programming Language" is split into three sections, which you can
 navigate through the menu on the left.
 
-## Basics
+<h2 class="section-header"><a href="basic.html">Basics</a></h2>
 
 This section is a linear introduction to the basic syntax and semantics of
 Rust. It has individual sections on each part of Rust's syntax, and culminates
@@ -17,15 +17,15 @@ in a small project: a guessing game.
 After reading "Basics," you will have a good foundation to learn more about
 Rust, and can write very simple programs.
 
-## Intermediate
+<h2 class="section-header"><a href="intermediate.html">Intermediate</a></h2>
 
 This section contains individual chapters, which are self-contained. They focus
 on specific topics, and can be read in any order.
 
 After reading "Intermediate," you will have a solid understanding of Rust,
 and will be able to understand most Rust code and write more complex programs.
 
-## Advanced
+<h2 class="section-header"><a href="advanced.html">Advanced</a></h2>
 
 In a similar fashion to "Intermediate," this section is full of individual,
 deep-dive chapters, which stand alone and can be read in any order. These